Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describe directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased octane and increased charge cooling due to its higher heat of vaporization compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. Further, water may be mixed with ethanol and/or used as an alternative to ethanol. The above approaches purport to improve engine fuel economy and increase utilization of renewable fuels.
One issue with the above approach is that requiring a user to always provide separate fuels (e.g., gasoline and ethanol) can be burdensome and impede wide-spread acceptance of such fuel economy improving technology. Therefore, in one approach, on-board vehicle separation may be used to take advantage of already available alcohol mixtures, such as E10 (10% ethanol and 90% gasoline) or E85 (85% ethanol and 15% gasoline), while taking advantage of delivering components of the mixture to the engine in varying ratios (and/or through different injectors), for example. However, since the user may provide varying concentrations (e.g., sometimes E85, sometimes E10, and/or sometimes gasoline), the separator may be adjusted based on operating conditions, such as based on the constituents in the fuel tank or engine usage rates. Further, it may be adjusted based on operating conditions of the engine and ambient conditions. In this way, it is possible to improve overall performance by adjusting separator operation to the particular operating conditions of the engine, environment, and supplied fuel mixture by the user.